What is a blower door?
A
blower door is a large calibrated fan that is
temporarily mounted in a house door to measure the
"leakiness" of the house and to assist in
finding the location of the leaks. Modern blower doors
have variable speed fans so that the pressure in the
house can be adjusted, and they also have door
mounting frames so that the fan can be sealed tightly
into the door jamb. In order to measure the leakiness
of the house, the blower door measures both the air
flow through the fan and the pressure difference
between the house inside and outside
What
does a blower door look like? GO
Why
should you care about air leakage in houses?
Everyone
knows that air leakage can cause uncomfortable drafts
in houses, but energy researchers have discovered that
sealing air leaks is one of the simplest and least
expensive way to save energy in homes. A typical house
may lose about 1/3 of its heat through walls and
ceilings, 1/3 through windows and doors, and 1/3
through air leakage. A few hours of air sealing with
inexpensive sealants can often reduce the air leakage
by about 1/4 to 1/2, resulting in a saving of 10% to
20% of the total house heating and cooling bill. Each
house has different amounts and types of air leakage,
and the most efficient technique is to spend the most
time sealing the leakiest houses. Duct leakage is
probably the worst type of house air leak. Therefore,
you need a tool that can quickly identify the leaky
houses and show you where the leaks are.
THE
PROBLEMS WITH LEAKAGE
Today,
many builders are routinely building houses that are
very airtight, often without realizing it. The common
use of building wraps, moisture barriers, high
efficiency windows and even simple plywood sheathing
all have direct effects on reducing air leakage and
infiltration. An airtight house has many fewer
openings through which fresh air can enter. Without
the addition of mechanical ventilation, a tight house
can result in stagnant air, less natural ventilation
and dissatisfied homeowners. On the other hand, houses
with large amounts uncontrolled air leakage are
equally troublesome with comfort complaints due to
drafts, building failures and high energy bills.
Despite
the growing importance of house air-tightness, few
builders, architects or homeowners know how tight
their houses are. Until recently, the building
community has tended to rely on subjective estimates
of air-tightness. Unfortunately, it is impossible to
accurately estimate the tightness level of a building
by visual inspection alone. And without knowing the
air-tightness level, it is difficult or impossible to
design for effective approaches to ventilation and air
quality, or to accurately diagnose performance
problems.
Why
is Building Leakage Important?
Building
tight houses without providing proper ventilation can
increase the potential for health and safety problems
to occurs. Higher moisture levels found in
inadequately ventilated houses create an ideal
environment for molds, dust mites and other causes of
respiratory problems and allergies. Tighter houses are
also more likely to experience problems from
back-drafting and spillage of combustion products from
naturally drafting furnaces, water heaters and
fireplaces. This is because in tight houses, it is
easier for exhaust devices (e.g. dryers, kitchen and
bath fans) to create large pressure differences
between inside and outside of the house, which can
interfere with proper venting of the combustion
appliances.
Leaky
houses have their own set of problems ranging from
drafts, blistering paint, ice dams and frozen pipes to
a house that won't adequately heat or cool. While in
the past airsealing efforts concentrated on the easy
to find air leaks around windows and door, we now know
that the most important leaks in a house are the hard
to find leaks in the attic, crawlspace, attached
garage and other framing connections. These hidden
leaks are responsible for most of the air leakage in
typical houses, and are often the cause of performance
and durability problems.
And
whether a house is tight or loose, nothing will cause
it to deteriorate faster than moisture migration and
condensation in attics, ceiling and other building
cavities. Vapor barriers will stop moisture diffusion,
but most moisture problems in buildings are a result
of uncontrolled air leakage through the building
envelope. And the way most vapor barriers are
installed, they do little or nothing to stop
uncontrolled air leakage. In many buildings, moisture
problems are made worse by the common use of hot tubs,
whirlpools and saunas.
Measuring
Building Airtightness
The
easiest way to measure building
